Not a direct answer to your question, but:

http://www.trainingandracingwithapowermeter.com/...s-skinny-vs-fat.html

That said, Cervelo claims in their P5 white paper that narrower head tubes aren't necessarily more aerodynamic.

At zero yaw, they are not more aero. They are more aero in crosswinds.... with 23mm tires. It the size and shape of the tires that drove the advantage in wider rims. A frame tube while it has structural requirements, is not constrained by a secondary function.... like holding a tire of a certain size.

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How wide will wheels go before it's a disadvantage?

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The short answer does not exist. The long answer is more nuanced that simply "wider is better".

Leading edge curvature that is properly designed can reduce or eliminate leading edge separation from high angle of attack flow. Simply "wider" is not necessarily better. Round profiles are pretty horrible, even if they're a combination of round + flat wedge.

In a perfect world the flow would naturally stay attached until at least the brake track, then the wheel profile can be wider, or trip the flow appropriately and mitigate separation at high yaw. If there was a reasonable way to get narrow tires mated to a rim such that the cross section is less like a tube and more like an oval or airfoil leading edge, then wheels could be just as efficient and narrower. In the current state of the art, wheels are designed to be wider than the tires that mount to them to achieve the same thing. The same constraint is not there for head tubes.

So then is there an advantage to steering systems that come out in front of the head tube in order to slim down the front profile? (Trek SC, DA/IA, P5 etc.)

The wheels are more about creating a continuous surface between the rim and tire So as not to create an "8" shape with tire bulge on skinny rims. That way your wheel looks more like a continuous oval or toroid or disc to the wind.

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Hello Red X and All,

http://www.view-speed.com/

In the San Diego Low Speed Wind Tunnel with a crosswind …….I saw a CDA of 0.19 on a P3 and regular tight fitting cycling jersey with older Zipps.

With a bit of effort that number could number be improved.

Frontal area will always be an important factor ..... as noted by Dr. Andrew Coggan reference.

Future rim/rolling surface gains in CDA should be possible with reduced frontal area …. maybe at the cost of some loss of riding comfort and handling.



The HPV data provides examples of the current envelope limits getting to CDA 0.11 and even further down to 0.055 for a faired bicycle.

http://www.legslarry.beerdrinkers.co.uk/tech/AeroDrag.htm

The information is dated as new speed records have been set. Some records posted here for HPV’s:

http://www.ihpva.org/hpvarec3.htm#nom01


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Cheers, Neal

+1 mph Faster

Wider isn't faster for tires/rims. With earlier wheels, people were still using 23c tires, so manufacturers made the fastest wheels to mate to them. A narrow tie/narrow wheel combo would be faster, it's just that a wide tire/narrow wheel is slower than wide tire/wide wheel.

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On that note, I did spot that Team BMC won the World Championship TTT in 2014 and were using standard H3 front wheels and Lightweight Disc wheels on the rear, mounted with Conti Podium 19mm tubs. No wide rims and no wide tyres, then. It did make me wonder a bit.

Cool link. I think your post had a typo. You mention the HPV data showing a CDA of 0.11 or 0.055. The link lists those as the _Cd_ (drag coefficient) and has another column for the frontal area and then another column showing them multiplied out for CdA, with the lowest being in the 0.02 range (about ten times lower than your P3 numbers).

I don't know sir, but it looks like a giant ...

http://www.youtube.com/watch?v=K1JgMxRm--0

Wider rims and tires are not more aero, but slightly wider tires do have a little bit less rolling resistance.

Unless physics has changed, all other things being equal, narrower is almost always more aero.

However, matching tire and rim widths is important.

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and, no... narrow tires still work better on wider rims than wide tires, aerodynamically, that is

 
Right, you want to use the best tire size/shape for your set up. Usually, but not always, that means a narrow tire, but of course these are all relative terms (what's 'narrow'? what's 'wide'?). In other words, matching tire and rim widths is important.

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sure, but a 20mm ss is still more aero than a 23mm or 25mm tire on an 808fc<=wide rim

 
Agreed, which means that 20mm is the best match tire width for FC 808s.
It's all about the right tire for the right rim.

But, all other things being equal (which they rarely are), narrow is nearly always better for reducing aero drag.

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Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
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When you can do 30+mph your yaw angle is going to be very different than someone averaging 20mph with the same wind conditions.


If you have a bike-rider system with a Cd vs. yaw plot that is not a constant you'll have an iterative loop:

1. As your speed changes your yaw angle changes.
2. As your yaw angle changes your Cd changes.
3. As your Cd changes your speed changes (for a given power output).
4. Repeat from step 1.

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Something else that I've been wondering about is what sort of yaw the rear wheel/tyre sees relative to the front wheel/tyre combo.

I can't recall ever seeing anything on this. But surely these are unlikely to be the same other than in the highly unlikely scenario of a 90 degree wind angle.

You also have to consider that wheel's leading edge also becomes a trailing edge. The other components don't have that same issue (unless you spend a lot of time riding backwards).

Most components just need to conform to a airfoil shape to have the best aerodynamics and size will be a relatively small issue.

You're correct, they will never be the same on the road. The front wheel is constantly moving to the left and right and it is constantly changing directions. Which means at times it will experience more yaw than the rear wheel and (more rarely) it will experience less yaw than the rear wheel. The only time that it might experience the same yaw as the rear would be on a fixed set up in a wind tunnel.

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It's not likely the same reason. It's more than the front wheel is in clean undisturbed air and will take a pure side gust + bicycle velocity, whereas the rear wheel is at least partially in the wake of flow that has be aligned with the bicycle's direction, and is not directly heading into the wind; the bicycle's downtube is handling this role. The rear wheel's job is likely best defined by how well the trailing edge minimizes its wake and separation from side gusts.

What you're saying is also correct.

But the fact that the front wheel is constantly moving into and out of the relative wind also partially accounts for the significant front/rear difference.

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Headtube maybe - anything that is a controlled or designed surface that precedes the rider I figure. The front wheel opens the envelope of the bike, which is why wider is better here, also for yaw I would think.

But in my hyper bike thread posted a while back ..."big" gains aren't going to be made with frames or parts. Gains can be made with automation and electro-mechanical manipulation of the bike to suit the conditions. One example is automatic shifting based on power and race course position. Attitude control of the bike to optimize RIDER aerodynamics & power output.

These ideas got no discussion or response when I posted them. You'd think with all the OCD about aero on the bike, someone would see possibilities in those ideas.

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That's not theoretically sound. I've explained it a bit in my first post here.

Nor consistent with actual data - see Fig. 5:

http://www.trainingandracingwithapowermeter.com/...aerodynamicists.html